California Resources Corporation (CRC) produces from the Wilmington Field in Southern California. For more than 50 years, water injection has been used successfully to abate subsidence and improve recovery. In recent years, they have revisited the topic of determining the ‘maximum allowable surface pressure’ for injection wells.
The Wilmington field consists of a series of unconsolidated sands interlayered with siltstones and shales. Injection is performed into the sands with permeability of 100-1000s of millidarcies. Because of their unconsolidated nature, the formations have strongly pressure dependent permeability (Davies and Davies, 1999). ResFrac is a fully 3D hydraulic fracturing and reservoir simulator, which makes it ideal for studying injection and the potential for hydraulic fracturing in high permeability formations. Conventional fracturing simulators use a 1D leakoff approximation, such as Carter leakoff, but in high permeability formations, flow quickly becomes elliptical or radial, and a 1D leakoff approximation is not realistic.
Running simulations under different rate and pressure scenarios, we investigated the potential for fracturing under different conditions. Because of the high permeability and the unconsolidated nature of the formation, if fractures did form, they would be very small and localized near the wellbore. The ResFrac simulations indicated that pressure transient analysis of shut-in data could be used to diagnose whether or not fractures are present. The simulations also showed the impact of pressure dependent permeability on the pressure trend during step-rate tests.
The simulations are helping CRC operate economically while also being good stewards of the environment, benefitting the local community.
Davies, J. P., & Davies, D. K. 1999. Stress-dependent permeability: characterization and modeling. Paper SPE-56813-MS presented at the SPE Annual Technical Conference and Exhibition, Houston, TX.
Kellogg, Ryan P., and David J. Mercier. 2019. Empirical Evidence Demonstrating Injection Containment and Absence of Injection Fracturing, Wilmington Oil Field Case study. Paper SPE-195-282-MS. Presented at the SPE Western Regional Meeting, San Jose, CA.